Morphological and structural design through hard-templating of PGM-free electrocatalysts for AEMFC applications.

This study delves into the critical role of customized materials design and synthesis methods in influencing the performance of electrocatalysts for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). It introduces a novel approach to obtain platinum-free (PGM-free) electrocatalysts based on the controlled integration of iron active sites onto the surface of silica nanoparticles (NPs) by using nitrogen-based surface ligands. These NPs are used as hard templates to form tailored nanostructured electrocatalysts with an improved iron dispersion into the carbon matrix. By utilizing a wide array of analytical techniques including infrared and X-ray photoelectron spectroscopy techniques, X-ray diffraction and surface area measurements, this work provides insight into the physical parameters that are critical for ORR electrocatalysis with PGM-free electrocatalysts. The new catalysts showed a hierarchical structure containing a large portion of graphitic zones which contribute to the catalyst stability. They also had a high electrochemically active site density reaching 1.47 × 1019 sites g-1 for SAFe_M_P1AP2 and 1.14 × 1019 sites g-1 for SEFe_M_P1AP2, explaining the difference in performance in fuel cell measurements. These findings underscore the potential impact of a controlled materials design for advancing green energy applications.

The Chemistry of Chelation for Built Heritage Cleaning: The Removal of Copper and Iron Stains.

Chelators are widely used in conservation treatments to remove metal stains from marble, travertine, and limestone surfaces. In the current review the chemical aspects underlying the use of chelators for the removal of copper and iron stains from built heritage are described and clear criteria for the selection of the most efficient stain removal treatment are given. The main chelator structural features are outlined and the operating conditions for effective metal stain removal (pH, time of application, etc.) discussed, with a particular emphasis on the ability to form stable metal complexes, the high selectivity towards the metal that should be removed, and the high sustainability for the environment. Dense matrices often host chelators for higher effectiveness, and further research is required to clarify their role in the cleaning process. Then, relevant case studies of copper and iron stain removal are discussed. On these bases, the most effective chelators for copper and stain removal are indicated, providing chemists and conservation scientists with scientific support for conservation operations on stone works of art and opening the way to the synthesis of new chelators.

Environmental Impact Prediction of a New Tire Vulcanization Activator.

Zinc oxide (ZnO) is the most common curing activator used to manufacture tires. To minimize environmental impacts by decreasing the zinc content and rolling resistance of tires, ZnO nanoparticles (NPs) anchored on SiO2 NPs (ZnO@SiO2) are currently under development as new activators at the pilot scale. Here, we applied prospective life cycle assessment to predict the impacts on human health, ecosystem quality, and resource scarcity of synthesizing ZnO@SiO2 for the production of passenger car tires at an industrial scale. We found that the life cycle impacts of the synthesis are expected to decrease by 89 to 96% between the pilot and industrial scale. The largest contributors to the synthesis of ZnO@SiO2 were electricity consumption and waste treatment of the solvent. Using the new activator for tire production led to potential reductions of 9 to 12% in life cycle impacts compared to tires that are currently in use. Those reductions were due to the expected decrease in rolling resistance, leading to lower fuel consumption, which outweighed the additional environmental impacts of the synthesis, as well as the potential decrease in lifetime. Our work highlights an opportunity for manufacturers to mitigate their impacts over the full life cycle of the tire.

Recent Advances on Porous Siliceous Materials Derived from Waste.

In recent years, significant efforts have been made in view of a transition from a linear to a circular economy, where the value of products, materials, resources, and waste is maintained as long as possible in the economy. The re-utilization of industrial and agricultural waste into value-added products, such as nanostructured siliceous materials, has become a challenging topic as an effective strategy in waste management and a sustainable model aimed to limit the use of landfill, conserve natural resources, and reduce the use of harmful substances. In light of these considerations, nanoporous silica has attracted attention in various applications owing to the tunable pore dimensions, high specific surface areas, tailorable structure, and facile post-functionalization. In this review, recent progress on the synthesis of siliceous materials from different types of waste is presented, analyzing the factors influencing the size and morphology of the final product, alongside different synthetic methods used to impart specific porosity. Applications in the fields of wastewater/gas treatment and catalysis are discussed, focusing on process feasibility in large-scale productions.

Mapping Understory Vegetation Density in Mediterranean Forests: Insights from Airborne and Terrestrial Laser Scanning Integration.

The understory is an essential ecological and structural component of forest ecosystems. The lack of efficient, accurate, and objective methods for evaluating and quantifying the spatial spread of understory characteristics over large areas is a challenge for forest planning and management, with specific regard to biodiversity and habitat governance. In this study, we used terrestrial and airborne laser scanning (TLS and ALS) data to characterize understory in a European beech and black pine forest in Italy. First, we linked understory structural features derived from traditional field measurements with TLS metrics, then, we related such metrics to the ones derived from ALS. Results indicate that (i) the upper understory density (5-10 m above ground) is significantly associated with two ALS metrics, specifically the mean height of points belonging to the lower third of the ALS point cloud within the voxel (HM1/3) and the corresponding standard deviation (SD1/3), while (ii) for the lower understory layer (2-5 m above ground), the most related metric is HM1/3 alone. As an example application, we have produced a map of forest understory for each layer, extending over the entire study region covered by ALS data, based on the developed spatial prediction models. With this study, we also demonstrated the power of hand-held mobile-TLS as a fast and high-resolution tool for measuring forest structural attributes and obtaining relevant ecological data.

Synthesis and Characterization of Alkoxysilane-Bearing Photoreversible Cinnamic Side Groups: A Promising Building-Block for the Design of Multifunctional Silica Nanoparticles.

The present study reports on the synthesis of a new alkoxysilane-bearing light-responsive cinnamyl group and its application as a surface functionalization agent for the development of SiO2 nanoparticles (NPs) with photoreversible tails. In detail, cinnamic acid (CINN) was activated with N-hydroxysuccinimide (NHS) to obtain the corresponding NHS-ester (CINN-NHS). Subsequently, the amine group of 3-aminopropyltriethoxysilane (APTES) was acylated with CINN-NHS leading to the generation of a novel organosilane, CINN-APTES, which was then exploited for decorating SiO2 NPs. The covalent bond to the silica surface was confirmed by solid state NMR, whereas thermogravimetric analysis unveiled a functionalization degree much higher compared to that achieved by a conventional double-step post-grafting procedure. In light of these intriguing results, the strategy was successfully extended to naturally occurring sepiolite fibers, widely employed as fillers in technological applications. Finally, a preliminary proof of concept of the photoreversibility of the obtained SiO2@CINN-APTES system has been carried out through UV diffuse reflectance. The overall outcomes prove the consistency and the versatility of the methodological protocol adopted, which appears promising for the design of hybrid NPs to be employed as building blocks for photoresponsive materials with the ability to change their molecular structure and subsequent properties when exposed to different light stimuli.

On the In Vitro and In Vivo Hazard Assessment of a Novel Nanomaterial to Reduce the Use of Zinc Oxide in the Rubber Vulcanization Process.

Zinc oxide (ZnO) is the most efficient curing activator employed in the industrial rubber production. However, ZnO and Zn(II) ions are largely recognized as an environmental hazard being toxic to aquatic organisms, especially considering Zn(II) release during tire lifecycle. In this context, aiming at reducing the amount of microcrystalline ZnO, a novel activator was recently synthetized, constituted by ZnO nanoparticles (NPs) anchored to silica NPs (ZnO-NP@SiO2-NP). The objective of this work is to define the possible hazards deriving from the use of ZnO-NP@SiO2-NP compared to ZnO and SiO2 NPs traditionally used in the tire industry. The safety of the novel activators was assessed by in vitro testing, using human lung epithelial (A549) and immune (THP-1) cells, and by the in vivo model zebrafish (Danio rerio). The novel manufactured nanomaterial was characterized morphologically and structurally, and its effects evaluated in vitro by the measurement of the cell viability and the release of inflammatory mediators, while in vivo by the Fish Embryo Acute Toxicity (FET) test. Resulting data demonstrated that ZnO-NP@SiO2-NP, despite presenting some subtoxic events, exhibits the lack of acute effects both in vitro and in vivo, supporting the safe-by-design development of this novel material for the rubber industry.

Photo- and radio-luminescence of porphyrin functionalized ZnO/SiO2 nanoparticles.

The development of hybrid nanoscintillators is hunted for the implementation of modern detection technologies, like in high energy physics, homeland security, radioactive gas sensing, and medical imaging, as well as of the established therapies in radiation oncology, such as in X-ray activated photodynamic therapy. Engineering of the physico-chemical properties of nanoparticles (NPs) enables the manufacture of hybrids in which the conjugation of inorganic/organic components leads to increased multifunctionality and performance. However, the optimization of the properties of nanoparticles in combination with the use of ionizing radiation is not trivial: a complete knowledge on the structure, composition, physico-chemical features, and scintillation property relationships in hybrid nanomaterials is pivotal for any applications exploiting X-rays. In this paper, the design of hybrid nanoscintillators based on ZnO grown onto porous SiO2 substrates (ZnO/SiO2) has been performed in the view to create nanosystems potentially suitable in X-ray activated photodynamic therapy. Indeed, cytotoxic porphyrin dyes with increasing concentrations have been anchored on ZnO/SiO2 nanoparticles through amino-silane moieties. Chemical and structural analyses correlated with photoluminescence reveal that radiative energy transfer between ZnO and porphyrins is the principal mechanism prompting the excitation of photosensitizers. The use of soft X-ray excitation results in a further sensitization of the porphyrin emission, due to augmented energy deposition promoted by ZnO in the surroundings of the chemically bound porphyrin. This finding unveils the cruciality of the design of hybrid nanoparticles in ruling the efficacy of the interaction between ionizing radiation and inorganic/organic moieties, and thus of the final nanomaterial performances towards the foreseen application.

Silica hairy nanoparticles: a promising material for self-assembling processes.

"Hairy" nanoparticles (HNPs), i.e. inorganic NPs functionalized with polymer chains, are promising building blocks for the synthesis of advanced nanocomposite (NC) materials having several technological applications. Recent evidence shows that HNPs self-organize in a variety of anisotropic structures, resulting in an improvement of the functional properties of the materials, in which are embedded. In this paper, we propose a three-step colloidal synthesis of spherical SiO2-HNPs, with controlled particle morphology and surface chemistry. In detail, the SiO2 core, synthesized by a modified Stöber method, was first functionalized with a short-chain amino-silane, which acts as an anchor, and then covered by maleated polybutadiene (PB), a rubbery polymer having low glass transition temperature, rarely considered until now. An extensive investigation by a multi-technique analysis demonstrates that the synthesis of SiO2-HNPs is simple, scalable, and potentially applicable to different kind of NPs and polymers. Morphological analysis shows the overall distribution of SiO2-HNPs with a certain degree of spatial organization, suggesting that the polymer coating induces a modification of NP-NP interactions. The role of the surface PB brushes in influencing the special arrangement of SiO2-HNPs was observed also in cis-1,4-polybutadiene (cis-PB), since the resulting NC exhibited the particle packing in "string-like" superstructures. This confirms the tendency of SiO2-HNPs to self-assemble and create alternative structures in polymer NCs, which may impart them peculiar functional properties.

Design of a Zn Single-Site Curing Activator for a More Sustainable Sulfur Cross-Link Formation in Rubber.

ZnO is a worldwide used activator for a rubber vulcanization process, which promotes fast curing kinetics and high cross-linking densities of rubber nanocomposites (NCs). However, its extended use together with leaching phenomena occurring during the production and life cycle of rubber products, especially tires, entails potential environmental risks, as ecotoxicity toward aquatic organisms. Pushed by this issue, a novel activator was developed, which introduces highly dispersed and active zinc species in the vulcanization process, reducing the amount of employed ZnO and keeping high the curing efficiency. The activator is constituted by Zn(II) single sites, anchored on the surface of SiO2 nanoparticles (NPs) through the coordination with functionalizing amino silane groups. It behaves as a double-function material, acting at the same time as a rubber reinforcing filler and a curing activator. The higher availability and reactivity of the single-site Zn(II) centers toward curative agents impart faster kinetics and higher efficiency to the vulcanization process of silica/isoprene NCs, compared to conventionally used ZnO activators. Moreover, the NCs show a high cross-linking degree and improved dynamic mechanical properties, despite the remarkably lower amount of zinc employed than that normally used for rubber composites in tires. Finally, the structural stability of Zn(II) single sites during the curing reactions and in the final materials may represent a turning point toward the elimination of zinc leaching phenomena.

Tailoring the Thermal Conductivity of Rubber Nanocomposites by Inorganic Systems: Opportunities and Challenges for Their Application in Tires Formulation.

The development of effective thermally conductive rubber nanocomposites for heat management represents a tricky point for several modern technologies, ranging from electronic devices to the tire industry. Since rubber materials generally exhibit poor thermal transfer, the addition of high loadings of different carbon-based or inorganic thermally conductive fillers is mandatory to achieve satisfactory heat dissipation performance. However, this dramatically alters the mechanical behavior of the final materials, representing a real limitation to their application. Moreover, upon fillers' incorporation into the polymer matrix, interfacial thermal resistance arises due to differences between the phonon spectra and scattering at the hybrid interface between the phases. Thus, a suitable filler functionalization is required to avoid discontinuities in the thermal transfer. In this challenging scenario, the present review aims at summarizing the most recent efforts to improve the thermal conductivity of rubber nanocomposites by exploiting, in particular, inorganic and hybrid filler systems, focusing on those that may guarantee a viable transfer of lab-scale formulations to technological applicable solutions. The intrinsic relationship among the filler's loading, structure, morphology, and interfacial features and the heat transfer in the rubber matrix will be explored in depth, with the ambition of providing some methodological tools for a more profitable design of thermally conductive rubber nanocomposites, especially those for the formulation of tires.

Morphology Related Defectiveness in ZnO Luminescence: From Bulk to Nano-Size.

This study addresses the relationship between material morphology (size, growth parameters and interfaces) and optical emissions in ZnO through an experimental approach, including the effect of different material dimensions from bulk to nano-size, and different excitations, from optical sources to ionizing radiation. Silica supported ZnO nanoparticles and ligand capped ZnO nanoparticles are synthesized through a sol-gel process and hot injection method, respectively. Their optical properties are investigated by radioluminescence, steady-state and time-resolved photoluminescence, and compared to those of commercial micrometric powders and of a bulk single crystal. The Gaussian spectral reconstruction of all emission spectra highlights the occurrence of the same emission bands for all samples, comprising one ultraviolet excitonic peak and four visible defect-related components, whose relative intensities and time dynamics vary with the material parameters and the measurement conditions. The results demonstrate that a wide range of color outputs can be obtained by tuning synthesis conditions and size of pure ZnO nanoparticles, with favorable consequences for the engineering of optical devices based on this material.

Grinding of composite cores using diamond burs with different grit sizes: the effects on the retentive strength of zirconia crowns

Aim: To evaluate the retention of Y-TZP crowns cemented in aged composite cores ground with burs of different grit sizes. Methods: Sixty composite resin simplified full-crown preparations were scanned, while 60 Y-TZP crowns with occlusal retentions were milled. The composite preparations were stored for 120 days (wet environment-37°C) and randomly distributed into three groups (n=20) according to the type of composite core surface treatment. The groups were defined as: CTRL (control: No treatment), EFB (extra-fine diamond bur [25µm]), and CB (coarse diamond bur [107µm]). The grinding was performed with an adapted surveyor standardizing the speed and pressure of the grinding. The intaglio surfaces on the crowns were air-abraded with silica-coated alumina particles (30 µm) and then a silane was applied. The crowns were cemented with self-adhesive resin cement, thermocycled (12,000 cycles; 5/55°C), stored (120 days) and submitted to a retention test (0.5mm/min). The retentive strength data (MPa) were analyzed using one-way analysis of variance and Tukey test, as well as Weibull analysis. Failures were classified as 50C (above 50% of cement in the crown), 50S (above 50% of cement in the substrate) and COE (composite core cohesive failure). Results: No statistical difference was observed among the retention values (p=0.975). However, a higher Weibull modulus was observed in the CTRL group. The predominant type of failure was 50S (above 50% of cement in the substrate composite). Conclusion: The retention of zirconia crowns was not affected by grinding using diamond burs with different grit sizes (coarse/extra-fine) or when no grinding was performed

Evaluation of the accuracy and stress distribution of 3-unit implant supported prostheses obtained by different manufacturing methods.

The purpose of this in vitro study was to measure the vertical, positive-horizontal, and negative-horizontal misfit (VM, PHM, and NHM, respectively) of the zirconia three-element prosthetic framework, fabricated using different methods, and compare them with conventional fabrication methods (lost-wax casting). Furthermore, this study aimed to evaluate the influence of the misfit values on the biomechanical behavior of the 3-unit fixed prosthetic frameworks using three-dimensional finite element analysis (3D-FEA). Forty frameworks (n = 10) were fabricated as follow: G1, Cerec Bluecam; G2, iTero; G3, 3Series; and G4, conventional method. The samples were randomized to measure marginal misfit using a high-precision three-dimensional (3D)-optical microscope. The results were submitted to analysis of variance (ANOVA), with the significance level set at 5%. The mean VM values of each group were used in creating the models by 3D-FEA with the misfit found in optical microscopy. The programs used were the InVesalius, Rhinoceros, SolidWorks, FEMAP and NEiNastran. The von Mises map was plotted for each model. The G4 showed the lowest mean VM value (16.73 µm), followed by G3 (20.71 µm), G2 (21.01 µm), and G1 (41.77 µm) (p < 0.001). G2 was more accurate than G1 (p < 0.05) and similar to G3 (p = 0.319). For PHM, G4 was the most accurate and did not present overextended values. With regard to NHM, the computer-aided design and computer-aided manufacturing (CAD-CAM) systems were more accurate (-61.91 µm) than G4 (-95.36 µm) (p = 0.014). In biomechanical analysis, stress concentration caused by oblique loading is greater than caused by axial loading. In axial loading, G4 was the most favorable while G1 was the least favorable, biomechanically, in oblique loading, similar stress patterns were observed in all the models. The prosthetic screw was the most overloaded structure, but the material did not influence the stress distribution. The misfit prostheses showed a greater degree of stress than the controls (without misfit). The manufacturing method influenced the marginal misfit of the frameworks, with the conventional method being the most accurate and the Cerec Bluecam System (closed system) the least accurate. Biomechanically, fitting prostheses were more favorable than misfit prostheses.

Hybrid Interface in Sepiolite Rubber Nanocomposites: Role of Self-Assembled Nanostructure in Controlling Dissipative Phenomena.

Sepiolite (Sep)⁻styrene butadiene rubber (SBR) nanocomposites were prepared by using nano-sized sepiolite (NS-SepS9) fibers, obtained by applying a controlled surface acid treatment, also in the presence of a silane coupling agent (NS-SilSepS9). Sep/SBR nanocomposites were used as a model to study the influence of the modified sepiolite filler on the formation of immobilized rubber at the clay-rubber interface and the role of a self-assembled nanostructure in tuning the mechanical properties. A detailed investigation at the macro and nanoscale of such self-assembled structures was performed in terms of the organization and networking of Sep fibers in the rubber matrix, the nature of both the filler⁻filler and filler⁻rubber interactions, and the impact of these features on the reduced dissipative phenomena. An integrated multi-technique approach, based on dynamic measurements, nuclear magnetic resonance analysis, and morphological investigation, assessed that the macroscopic mechanical properties of clay nanocomposites can be remarkably enhanced by self-assembled filler structures, whose formation can be favored by manipulating the chemistry at the hybrid interfaces between the clay particles and the polymers.

Survival rate and load to failure of premolars restored with inlays: An evaluation of different inlay fabrication methods.

STATEMENT OF PROBLEM: Studies that evaluate the survival rate and load to fracture of premolars restored with inlays produced using different methods are lacking. PURPOSE: The purpose of this in vitro study was to compare the survival rate and fracture load of premolars restored with inlays fabricated using different methods. MATERIAL AND METHODS: Thirty maxillary premolars were selected, embedded, and prepared to receive inlays fabricated using different methods (n=10): LaCom-digital scanning with Lava C.O.S. scanner (3M ESPE), followed by milling of composite resin block (Lava Ultimate; 3M ESPE) in a milling unit; CeCom-digital scanning with Cerec 3D Bluecam scanner (Dentsply Sirona), followed by milling of a Lava Ultimate block in Cerec (Dentsply Sirona); PresDis-impression with polyvinyl siloxane, inlay made using the lost wax technique, and IPS e.max Press (Ivoclar Vivadent AG) pressed ceramic (lithium disilicate). A dual-polymerizing resin cement system was used to lute the inlays. Inlays were mechanically cycled (2 Hz, 106 mechanical pulses, 80 N) after 24 hours, and the specimens were stored in distilled water at 37°C for 11 months. Then, a fatigue test was conducted using a 10-Hz frequency and 400-N load on the inner inclines of the cusps. The test was complete when the specimen fractured or when the specimen reached 1.5×106 cycles. The specimens that survived fatigue testing were submitted to a single-load fracture test in a universal testing machine and analyzed using a stereoscope for failure classification. Survival rates were estimated using the Kaplan-Meier method and log-rank test (Mantel-Cox). Fracture load data were analyzed using 1-way ANOVA (α=.05). RESULTS: No significant differences were detected among the groups for the survival rate (P=.87) or for the load to fracture (P=.78). Most failures were longitudinal, catastrophic fractures. CONCLUSIONS: Premolars restored with inlays fabricated using the tested methods had similar survival rates and loads to fracture.

Prosthetically CAD-CAM-Guided Bone Augmentation of Atrophic Jaws Using Customized Titanium Mesh: Preliminary Results of an Open Prospective Study.

This study evaluated the outcomes of computer-aided design-computer-aided machining (CAD-CAM)-customized titanium mesh used for prosthetically guided bone augmentation related to the occlusion-driven implant position, to the vertical bone volume gain of the mandible and maxilla, and to complications, such as mesh exposure. Nine patients scheduled for bone augmentation of atrophic sites were treated with custom titanium mesh and particulate bone grafts with autologous bone and anorganic bovine bone in a 1:1 ratio prior to implant surgery. The bone volume needed to augment was virtually projected based on implant position, width, and length, and the mesh design was programmed for the necessary retaining screws. After 6 to 8 months, bone augmentations of 1.72 to 4.1 mm (mean: 3.83 mm) for the mandibular arch and 2.14 to 6.88 mm (mean: 3.95 mm) for the maxilla were registered on cone-beam computerized tomography. Mesh premature (within 4 to 6 weeks) exposure was observed in 3 cases and delayed (after 4 to 6 weeks) in 3 other cases. One titanium mesh was removed before the programmed time but in all augmented sites was possible implant insertion. No complication occurred during prosthetic follow-up. Using CAD-CAM technology for prosthetically guided bone augmentation showed important postoperative morbidity of mesh exposure (66%). Because of this high prevalence of mesh exposure and the potential infection that could affect the expected bone augmentation, this study suggests a cautious approach to this procedure when designing the titanium mesh, to avoid flap tension that may cause mucosal rupture.

A Green Approach for Preparing High-Loaded Sepiolite/Polymer Biocomposites.

Global industry is showing a great interest in the field of sustainability owing to the increased attention for ecological safety and utilization of renewable materials. For the scientific community, the challenge lies in the identification of greener synthetic approaches for reducing the environmental impact. In this context, we propose the preparation of novel biocomposites consisting of natural rubber latex (NRL) and sepiolite (Sep) fibers through the latex compounding technique (LCT), an ecofriendly approach where the filler is directly mixed with a stable elastomer colloid. This strategy favors a homogeneous dispersion of hydrophilic Sep fibers in the rubber matrix, allowing the production of high-loaded sepiolite/natural rubber (Sep/NR) without the use of surfactants. The main physicochemical parameters which control Sep aggregation processes in the aqueous medium were comprehensively investigated and a flocculation mechanism was proposed. The uniform Sep distribution in the rubber matrix, characteristic of the proposed LCT, and the percolative filler network improved the mechanical performances of Sep/NR biocomposites in comparison to those of analogous materials prepared by conventional melt-mixing. These outcomes indicate the suitability of the adopted sustainable procedure for the production of high-loaded clay⁻rubber nanocomposites with remarkable mechanical features.

Unveiling the hybrid interface in polymer nanocomposites enclosing silsesquioxanes with tunable molecular structure: Spectroscopic, thermal and mechanical properties.

Organic-inorganic nanobuilding blocks (NBBs) based on silsesquioxanes (SSQs) have potential applications as nanofillers, thermal stabilizers, and rheological modifiers, which can improve thermomechanical properties of polymer hosts. The possibility to tune both siloxane structure and pendant groups can promote compatibilization and peculiar interactions with a plethora of polymers. However, the control on SSQs molecular architecture and functionalities is usually delicate and requires careful synthetic details. Moreover, investigating the influence of NBBs loading and structure on the hybrid interface and, in turn, on the polymer chains mobility and mechanical properties, may be challenging, especially for low-loaded materials. Herein, we describe the preparation and characterization of polybutadiene (PB) nanocomposites using as innovative fillers thiol-functionalized SSQs nanobuilding blocks (SH-NBBs), with both tailorable functionality and structure. Swelling experiments and, more clearly, solid-state NMR, enlightened a remarkable effect of SH-NBBs on the molecular structure and mobility of the polymeric chains, envisaging the occurrence of chemical interactions at the hybrid interface. Finally, thermal and DMTA analyses revealed that nanocomposites, even containing very low filler loadings (i.e. 1, 3 wt%), exhibited enhanced thermomechanical properties, which seem to be connected not only to the loading, but also to the peculiar cage or ladder-like architecture of SH-NBBs.

Zirconia-based versus metal-based single crowns veneered with overpressing ceramic for restoration of posterior endodontically treated teeth: 5-year results of a randomized controlled clinical study.

OBJECTIVES: The aim of this 5-year randomized controlled trial was to compare the longevity and clinical behavior of single posterior crowns made with pressable ceramic on zirconia and on metal frameworks, and if failures occur, to delineate the contributing factors. METHODS: 72 patients, who needed the covering of at least a molar and/or premolar, were included in the study. All teeth were endodontically treated, with absence of periapical lesion or active periodontitis. Ninety single crowns were made with zirconia or metal framework and covered with pressable veneering ceramics. Two independent examiners assessed the survival of restorations at 6 months, 1-4 and 5 years after restoration placement including periapical radiographs, intraoral photographs, and USPHS modified criteria. The statistical analyses were performed with the Kaplan-Meier method. RESULTS: One core fracture occurred in Zircad/Zirpress crowns and one metal ceramic crown was lost for root fracture. Chipping fracture of the veneering ceramic was detected in 2 metal-ceramic crowns and in 3 zirconia-based crowns. The Estimate Cumulative Survival (ECS) and the Estimate Cumulative Success (ECSs) with standard deviation (SE) were respectively 97,73±2,19 and 92,64±4,14 for zirconia-based crowns whereas 97,44±2,39 and 91,11±4,27 for porcelain fused to metal crowns. CONCLUSIONS: The present randomized controlled trial shows that the survival of zirconia-based and metal-based single crowns is similar over a follow-up period of 5 years. No significant differences in esthetic, functional and biological outcomes were demonstrated between the two groups. The main failure mode was the chipping fracture of the veneering ceramic in both materials. Study number on ClinicalTrial.gov NCT02758457. CLINICAL SIGNIFICANCE: According to the results of this clinical study, zirconia-based rehabilitations with overpressing veneering technique represent a valid alternative to metal-based for posterior single crown restorations.